Manures and the principles of manuring

by Charles Morton Aikman

To recapitulate, the chief physical or mechanical properties of a soil are its absorptive and retentive powers for water; its capacity for heat; and its power of absorbing gases. It will be easily seen how tillage operations are calculated to influence these physical properties of a soil. Thus, in the case of a stiff soil, tillage increases its power for absorbing the atmospheric gases, chiefly oxygen, which are so necessary for rendering its fertilising matters available. On the other hand, in a light and too open soil it may exert quite a contrary effect.

It may be also well to refer here to the important influence these physical properties exercise on the growth of the plant.

Plant-roots require a certain Openness in the Soil.

One of the functions of the soil is to support the plant in an upright position, and this is a function which requires in the soil a certain amount of compactness or firmness. On the other hand, however, a soil must not possess too great compactness, otherwise the plant-roots will experience a difficulty in pushing their way downwards. This is especially the case during the earlier periods of growth, when the plant-roots are as yet extremely tender, and experience great difficulty in overcoming much resistance. The importance of preparing a mellow seed-bed will be thus at once seen to be based on sound scientific principles; and this for a double reason. Not only does the young plant require every facility for developing its roots, but also, as has just been pointed out, an abundant supply of oxygen is of paramount importance during the process of germination.

Soil and Plant-roots.

The whole question of the influence of the mechanical condition of the soil on the development of plant-roots is one of the highest importance and interest, and is not so generally recognised as it ought to be.

Natural tendency of Plant-roots to grow downwards.

It may be taken as certain that the tangled condition of plant-roots is due to the resistance offered by the soil-particles, and that the natural tendency of the plant-root is to grow downwards. The roots, in short, would probably grow in as symmetrical a form as do the stalks or branches, were it not that they are hindered from so doing by the soil-particles. Where, then, the soil is such as to offer much hindrance, the growth of the plant cannot but be retarded. Some extremely interesting experiments have been performed by the eminent German chemist Hellriegel on the influence which the closeness of the soil-particles has on root-development. In these experiments peas and beans were grown in moistened sawdust, more or less compactly compressed. It was found that when the sawdust Was compressed to any extent, plant-growth took place very slowly, or entirely ceased.

The importance of having plant-roots as widely developed in the soil as possible, will be at once seen when we reflect that this means that the area of soil from which the plant derives its soil-food is thereby greatly increased. Another important consideration is, that the deeper plant-roots can penetrate in a soil, the more able—other conditions being equal—is the plant to withstand the action of drought, as it can draw water for its needs from the deeper layers of the soil, long after a plant, whose roots do not penetrate so deeply, has wilted.

Plants require Room.